Water Injection and Venting of a Plasma Arc Torch

ABSTRACT

A plasma arc torch system comprising a plasma arc torch is provided. The torch includes an electrode, a nozzle, a vent passage and a shield. The nozzle is spaced from the electrode to define a plasma chamber therebetween. The plasma chamber is configured to receive a plasma gas. The vent passage, disposed in the nozzle body, is configured to divert a portion of the plasma gas exiting the plasma chamber from a nozzle exit orifice. The shield is spaced from the nozzle to define a flow region therebetween. The flow region is configured to (i) receive a liquid and (ii) expel the liquid along with a plasma arc substantially surrounded by the liquid via a shield exit orifice.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of Ser. No. 14/567,387,filed on Dec. 11, 2014 and entitled “Water Injection and Venting of aPlasma Arc Torch,” the entire content of which is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to an improved plasma arc torchsystem and an improved approach for operating the plasma arc torchsystem.

BACKGROUND OF THE INVENTION

Thermal processing torches, such as plasma arc cutting torches, arewidely used in the cutting, gouging and marking of materials. A plasmaarc torch generally includes an electrode, a nozzle having a centralexit orifice mounted within a torch body, electrical connections,passages for cooling, and passages for arc control fluids (e.g., plasmagas). Optionally, a swirl ring is employed to control fluid flowpatterns in the plasma chamber formed between the electrode and thenozzle. In some torches, a retaining cap can be used to maintain thenozzle and/or swirl ring in the plasma arc torch. In operation, thetorch produces a plasma arc, which is a constricted jet of mostlyionized gas with high temperature and that can have sufficient momentumto assist with removal of molten metal.

Traditionally, a plasma arc torch can cut metal workpieces (e.g.,stainless steel or aluminum workpieces) using a plasma gas, such asnitrogen N₂, a mixture of 35% hydrogen and 65% argon (H35), or a mixtureof 95% nitrogen and 5% hydrogen (F5). Because these gases are relativelyexpensive to produce and obtain, they can increase the overall cost oftorch operations. In addition, cut speeds are limited by cut qualityconsiderations.

SUMMARY OF THE INVENTION

Thus, systems and methods are needed to enhance plasma arc torchperformance by (i) reducing cost, especially in cutting operations, and(ii) improving cut quality for high-speed operations. As explainedbelow, the simultaneous use of multiple arc constricting techniques canresult in exceptional cutting results. For example, embodiments of theinvention improve cutting operations by using a plasma arc torch that isequipped with a vented nozzle and provided with a liquid (e.g., water)as shield fluid. Such a combination reduces operation cost whileachieving higher cut speed and enhanced cut quality. The reduced cost ispartly due to the use of inexpensive fluids (e.g., N₂ plasma gas and/orwater shield fluid) as a cutting medium, which is much cheaper thanusing traditional fluids (e.g., H35 or F5 plasma gas and N2 shield gas).The present technology also includes an efficient shield fluid deliverysystem configured to promote higher cut speed and better cut edgeappearance.

In one aspect, a plasma arc torch system comprising a plasma arc torchis provided. The torch includes an electrode, a nozzle, a vent passage,and a shield. The nozzle is spaced from the electrode to define a plasmachamber therebetween. The nozzle comprises a nozzle body and a nozzleexit orifice. The plasma chamber is configured to receive a plasma gas.The vent passage, disposed in the nozzle body, is configured to divert aportion of the plasma gas exiting the plasma chamber from the nozzleexit orifice. The shield is spaced from the nozzle to define a flowregion therebetween. The shield comprises a shield exit orifice in fluidcommunication with the nozzle exit orifice. The flow region isconfigured to (i) receive a liquid and (ii) expel the liquid along witha plasma arc substantially surrounded by the liquid via the shield exitorifice.

In some embodiments, the plasma arc torch system further comprises asupply system that includes a liquid source for supplying the liquid, aliquid supply conduit for conducting the liquid from the liquid sourceto the torch, and an activation valve disposed between the liquid sourceand the torch along the liquid supply conduit. The activation valve isconfigured to enable or disable a flow of the liquid to the flow region.The supply system of the plasma arc torch system can include a pressureregulator coupled to the liquid supply conduit for regulating a liquidpressure value associated with a flow of the liquid in the liquid supplyconduit. The supply system can include a flow valve disposed between theliquid source and the torch along the liquid supply conduit. The flowvalve is configured to regulate a flow rate of the flow of the liquid inthe liquid supply conduit. The supply system can include a flow meterdisposed between the liquid source and the torch along the liquid supplyconduit. The flow meter is configured to measure a flow rate of the flowof the liquid in the liquid supply conduit. The plasma arc torch systemcan further include a gas supply conduit configured to supply a shieldgas from a gas source to the flow region and a shield fluid conduitformed by joining the gas supply conduit and the liquid supply conduitdownstream from the activation valve. The shield fluid conduit isconfigured to convey one of the shield gas from the gas supply conduitor the liquid from the liquid supply conduit to the flow regiondepending on an operator selection.

In some embodiments, the plasma arc torch system further comprises asupply system that includes a liquid supply conduit for conducting theliquid from a liquid source to the torch, a pressure regulator coupledto the liquid supply conduit, a flow valve disposed between the liquidsource and the torch along the liquid supply conduit, and an activationvalve disposed between the liquid source and the torch along the liquidsupply conduit. The pressure regulator is configured to regulate aliquid pressure value associated with a flow of the liquid in the liquidsupply conduit. The flow valve is configured to regulate a flow rate ofthe flow of the liquid in the liquid supply conduit. The activationvalve is configured to enable or disable the flow of the liquid to theflow region. The supply system can also include an optional flow meterconfigured to measure the flow rate of the flow of the liquid in theliquid supply conduit.

In some embodiments, the plasma arc torch system further comprises asupply system that includes a liquid supply conduit for conducting theliquid from a liquid source to the torch, a pressure regulator coupledto the liquid supply conduit and an activation valve disposed betweenthe liquid source and the torch along the liquid supply conduit. Thepressure regulator is configured to regulate a liquid pressure valueassociated with a flow of the liquid in the liquid supply conduit. Theactivation valve is configured to enable or disable the flow of theliquid to the flow region. The supply system can also include anoptional flow meter configured to measure a flow rate of the flow of theliquid in the liquid supply conduit.

In some embodiments, the plasma arc torch system further comprises asupply system that includes a liquid supply conduit for conducting theliquid from a liquid source to the torch, a flow valve disposed betweenthe liquid source and the torch along the liquid supply conduit, anactivation valve disposed between the liquid source and the torch alongthe liquid supply conduit, and a flow meter disposed between the liquidsource and the torch along the liquid supply conduit. The flow valve isconfigured to regulate a flow rate of a flow of the liquid in the liquidsupply conduit. The activation valve is configured to enable or disablethe flow of the liquid to the flow region. The flow meter is configuredto measure the flow rate of the flow of the liquid in the liquid supplyconduit.

In some embodiments, the vent passage has an inlet located upstream fromthe nozzle exit orifice. In some embodiments, the shield exit orifice issubstantially aligned with the nozzle exit orifice to define a conduitfor expelling the liquid, the plasma arc and an unionized portion of theplasma gas.

In some embodiments, the nozzle exit orifice is configured to constrictthe plasma arc exiting the plasma chamber to the flow region via thenozzle exit orifice. In some embodiments, the vent passage in the nozzleand the liquid in the flow region provide constriction on the plasmaarc. The swirling motion of the plasma gas can further constrict theplasma arc.

In another aspect, a method is provided for operating a plasma arc torchto cut a workpiece. The method includes passing a plasma gas to a plasmachamber in the torch defined by an electrode and a nozzle, ionizing afirst portion of the plasma gas to form a plasma arc in the plasmachamber, and venting a second portion of the plasma gas via at least onevent passage disposed in the nozzle. The method also includes passingthe plasma arc from the plasma chamber to a flow region via a nozzleexit orifice. The flow region is defined by the nozzle and a shield. Themethod further includes supplying a liquid to the flow region via aconduit located between the nozzle and the shield and directing theliquid from the conduit to substantially surround the plasma arc.

In some embodiments, ionizing the first portion of the plasma gasfurther comprises passing a current between the electrode and thenozzle.

In some embodiments, constriction of the plasma arc is provided by atleast one of i) the venting, ii) the nozzle exit orifice before theplasma arc passes to the flow region, iii) the liquid that substantiallysurrounds the plasma arc in the shield exit orifice, or iv) the swirlingmotion of the plasma gas.

In some embodiments, the method further includes shearing, by theliquid, in a liquid or vapor state, molten material away from aworkpiece being processed by the plasma arc. The method can furtherinclude reducing, by the liquid, a heat affected zone generated duringprocessing of a workpiece by the plasma arc.

In yet another aspect, a plasma arc torch is provided that includes atorch body and a tip assembly connected to the torch body. The tipassembly includes an electrode, a nozzle disposed about the electrode,and a shield disposed about the nozzle. The nozzle includes (1) a nozzleexit orifice and (2) a vent conduit having an inlet located upstreamfrom the nozzle exit orifice. The shield includes a shield exit orifice.The nozzle and the shield define a flow region therebetween, where theflow region is shaped to expel a liquid along with a plasma arc that issubstantially surrounded by the liquid through the shield exit orifice.

In some embodiments, the plasma arc torch further includes a supplysystem in fluid communication with the flow region. In some embodiments,the shield comprises a conduit for receiving the liquid and introducingthe liquid to the flow region. In some embodiments, constriction of theplasma arc is provided by at least one of the nozzle exit orifice, theventing, the liquid as the plasma arc passes via the shield exit orificeor the swirling motion of the plasma gas.

In other examples, any of the aspects above can include one or more ofthe following features. In some embodiments, the plasma gas is at leastone of nitrogen, F5 or air. In some embodiments, the liquid is water. Insome embodiments, a combination of the electrified ionized plasma gasand the liquid produces hydrogen.

It should also be understood that various aspects and embodiments of theinvention can be combined in various ways. Based on the teachings ofthis specification, a person of ordinary skill in the art can readilydetermine how to combine these various embodiments. For example, in someembodiments, any of the aspects above can include one or more of theabove features. One embodiment of the invention can provide all of theabove features and advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages of the invention described above, together with furtheradvantages, may be better understood by referring to the followingdescription taken in conjunction with the accompanying drawings. Thedrawings are not necessarily to scale, emphasis instead generally beingplaced upon illustrating the principles of the invention.

FIG. 1 shows an exemplary plasma arc torch, according to someembodiments of the present technology.

FIG. 2 shows an exemplary shield liquid flow path, according to someembodiments of the present technology.

FIG. 3 shows an exemplary shield fluid supply system, according to someembodiments of the present technology.

FIG. 4 shows another exemplary shield fluid supply system, according tosome embodiments of the present technology.

FIG. 5 shows an exemplary method for operating the plasma arc torch ofFIGS. 1 and 2.

FIG. 6 shows cut results on exemplary stainless steel workpieces usingthe systems and methods described above with reference to FIGS. 1-5.

FIG. 7 shows cut results on exemplary aluminum workpieces using thesystems and methods described above with reference to FIGS. 1-5.

FIG. 8 shows cut results on another set of stainless steel workpiecesusing the systems and methods described above with reference to FIGS.1-5.

FIGS. 9A and B show various views of cut results on yet another set ofstainless steel workpieces using the systems and methods described abovewith reference to FIGS. 1-5.

FIG. 10 shows cut results on yet another set of stainless steelworkpieces using the systems and methods described above with referenceto FIGS. 1-5.

FIG. 11 shows a percentage speed improvement comparison chart fordifferent processes.

FIG. 12 shows a normalized cutting speed comparison chart for differentprocesses.

FIG. 13 shows a comparison of workpiece surface roughness and wavinessproduced by different processes.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an exemplary plasma arc torch, according to someembodiments of the present technology. A plasma arc torch can include atorch body 101 and a tip assembly 90 connected to the torch body 101.The tip assembly 90 can include a nozzle 100, a swirl ring 105, anelectrode 110, and a plasma chamber 130. The torch defines a distal end205, which is the end that is positioned closest to a workpiece (notshown) during torch operation. The electrode 110 has a distal end face140 and an exterior surface 150. The plasma chamber 130 is defined, atleast in part, by the distal end face 140 of the electrode 110 and thenozzle 100, which is situated in a spaced relationship from theelectrode 110. The plasma chamber 130 is configured to receive a plasmagas.

The nozzle 100 includes a body 115, a liner 120 disposed within the body115, and at least one plasma gas vent passage 125 formed in the body115. The body 115 of the nozzle 100 can have a nozzle exit orifice 195at the distal end 205. The liner 120 can include a liner exit orifice215 between a distal end face of electrode 140 and the nozzle exitorifice 195 (e.g., at distal end 205 adjacent nozzle exit orifice 195).In some embodiments, the diameter of the nozzle exit orifice 195 isreduced to produce high-current densities and better plasma-arcconstriction to promote enhanced cut quality and cutting speed.

The vent passage 125 in the nozzle 100 can have an inlet 225 and anoutlet 230. In some embodiments, the vent passage 125 is a vent hole.The vent passage 125 is in fluid communication with a venting channel180 disposed in the nozzle 100. The venting channel is configured todirect a portion of a plasma gas exiting the plasma chamber 130, frombetween the liner exit orifice 215 and the nozzle exit orifice 195 tothe plasma gas vent passage 125 of the nozzle 100. The plasma gas ventpassage 125 can be disposed adjacent the venting channel 180 and withthe inlet 225 and the outlet 230 positioned upstream from the nozzleexit orifice 195.

The swirl ring 105 is in fluid communication with the plasma chamber130. The swirl ring 105 has an exterior surface 155, an interior surface160, at least one proximal inlet gas opening 235, and at least onedistal outlet gas port 135 (e.g., a swirl injection point, swirl hole,etc.). The exterior surface 155 of the swirl ring 105 and interiorsurface of the torch body 101 can define at least in part an inner gaschamber 175. The proximal inlet gas opening 235 can extend to the innergas chamber 175 to provide a gas to the inner gas chamber 175. The innergas chamber 175 can be in fluid communication with the distal outlet gasport 135 to provide the gas from the inner gas chamber 175 to the plasmachamber 130 and generate a substantially swirling gas flow in the plasmachamber 130.

The torch of FIG. 1 can also include a shield 300 spaced from the nozzle100. The shield 300 includes a shield exit orifice 304 in fluidcommunication with the nozzle exit orifice 195. The shield exit orifice304 can be substantially aligned and coaxial with the nozzle exitorifice 195 to define a flow region 302 therebetween. The shield 300 canalso include a liquid passageway 306 between the nozzle 100 and theshield 300 that allows a shield liquid (e.g., water) to be introducedinto the flow region 302. In some embodiments, the shield liquid may beintroduced into flow region 302 via an opening (not shown) disposed inthe body of the shield, where the opening is in fluid communication withthe passageway 306. Specifically, the liquid passageway 306 is definedby an external surface of the nozzle body 115 and an internal surface ofthe shield 300. In some embodiments, the liquid passageway is defined byan external surface of the nozzle body 115 and an internal surface ofthe shield cap 301.

FIG. 1 also shows a plasma gas flow path 181, according to someembodiments of the present technology. Exemplary plasma gas includes atleast one of nitrogen, F5 or air. The plasma gas is introduced into thetorch through the inlet gas opening 235 (e.g., metering or distributionholes) of the swirl ring 105 into the inner gas chamber 175. The plasmagas is directed to the distal outlet gas port 135 that provides the gasfrom the inner gas chamber 175 to the plasma chamber 130. The distaloutlet gas port 135 can generate a substantially swirling gas flow inthe plasma chamber 130.

During torch operation, a portion of the plasma gas in the plasmachamber 130 can be ionized by an electrical current provided to theelectrode 110, which acts as a cathode, and the nozzle 100, which actsas an anode, to generate a plasma arc in the plasma chamber 130. Anelectric arc that is formed between the electrode 110 and the nozzle 100in the plasma chamber 130 can generate high heat that in turn ionizes atleast a portion of the plasma gas introduced by the distal outlet gasport 135. The electric arc and the ionized gas constitute the plasma arc(i.e., an ionized gas jet). The plasma arc can be applied to a workpieceto mark, cut, or otherwise operate on the workpiece when the arc isexpelled from the gas chamber 130 to the flow region 302 via the nozzleexit orifice 195 and from the flow region 302 to the outside via theshield exit orifice 304.

In some embodiments, a portion of the plasma gas introduced by thedistal outlet gas port 135 into the plasma chamber 130 can remain in itsunionized form (i.e., not ionized by the electric arc to form a part ofthe plasma arc). Hereinafter, this portion of the plasma gas is referredas as a unionized plasma gas. The unionized plasma gas can be expelled,along with the plasma arc, from the gas chamber 130 to the flow region302 via the nozzle exit orifice 195 and from the flow region 302 to theoutside via the shield exit orifice 304.

In some embodiments, the swirling motion of the plasma gas provided bythe swirl ring 105 stabilizes the plasma arc inside of the plasmachamber 130. In particular, as the plasma gas rotates in plasma chamber130, the hotter, lighter portion of the plasma gas remains near thecenter of the plasma chamber 130, while the cooler, heavier portion ofthe plasma gas is driven to the outer walls of the chamber 130 bycentrifugal force. Such temperature gradients generate a thermal pinch.In addition, the swirling plasma gas generates higher pressure along theouter wall of the plasma chamber 130 and lower pressure at the center,thus creating a pressure gradient in the chamber 130 to squeeze theplasma arc, thereby creating a pressure pinch that constricts the plasmaarc in the plasma chamber 130, which can improve cut performance. Arcconstriction is also provided by thermal considerations governed by thesize of the emitter in the electrode 110 and the cooling of the emitter.In addition, using a nozzle exit orifice with a small diameter, whichexpels only a small fraction of the plasma gas from the plasma chamber130 to the flow region 302, further enhances constriction on the plasmaarc.

As shown by the plasma gas flow path 181, after the plasma arc and/orthe unionized plasma gas exit the plasma chamber 130, a portion of theunionized gas can be diverted through the venting channel 180, to coolthe nozzle 100, and directed to at least one vent gas passage 125 in thenozzle 100. In some embodiments, the vented gas can be directed throughthe venting channel 180, passing between the liner 120 and the nozzlebody 115 (e.g., nozzle shell). Then, the vented gas can pass through thegas vent passage 125 (e.g., metering holes, vent holes, etc.) to a torchvent gas conduit and out to ambient atmosphere. In some embodiments, theventing provided by the venting channel 180 and the gas vent passage 125constricts the plasma arc upstream of the nozzle exit orifice 195between the liner 120 and the nozzle body 115. In addition, the ventingvia vent gas passage 125 can promote cooling of the nozzle 100.

FIG. 2 shows an exemplary shield liquid flow path 182, according to someembodiments of the present technology. The configuration of the plasmaarc torch of FIG. 2 is substantially the same as that the plasma arctorch of FIG. 1. The shield liquid can comprise water, for example. Asshown, the shield liquid is introduced into the torch through an opening(not shown) disposed in the body of the shield 300. The shield liquidcan flow into the liquid passageway 306 that is in fluid communicationwith the opening. The shield liquid is directed by the liquid passageway306 to the flow region 302 situated between the nozzle exit orifice 195and the shield exit orifice 304. The flow region 302 can expel theshield liquid out of the torch via the shield exit orifice 304. In someembodiments, a lower shield swirl strength is used with shield liquids(e.g. water) in comparison to the use of shield gases in the samecutting process

In some embodiments, the shield liquid impinges on the plasma arc and/orunionized plasma gas that are ejected by the nozzle exit orifice 195from the plasma chamber 130. The shield liquid can substantiallysurround the plasma arc. In some embodiments, the shield liquidconstricts the plasma arc as the liquid and the arc pass through theshield exit orifice 304. The use of a shield liquid is advantageousbecause at a high flow rate, a shield gas is compressible, while ashield liquid is not. Therefore, higher constriction of the plasma arccan be achieved with shield liquid as opposed to shield gas. Inaddition, a dense shield liquid, such as water, provides even betterconstriction. There are additional advantages associated with usingwater as a shield fluid. For example, as water comes into contact withhigh temperature plasma, a portion of it decomposes into oxygen andhydrogen, where the hydrogen interacts with the plasma cutting processto give the kerf of a cut a color closer to that of the base material incomparison to a cut made with cutting processes using nitrogen or airplasma gas in combination with nitrogen or air shield gas. In addition,water, being a denser matter compared to a gas, helps in shearing (e.g.,pushing) molten metal away from the workpiece being cut. This results ina smooth, dross-free cut. Furthermore, using water as a shield fluidreduces the heat that can spread into the workpiece, thereby reducingthe extent of heat affected zone.

FIG. 3 shows an exemplary shield fluid supply system, according to someembodiments of the present technology. The supply system 400 can delivera shield liquid, such as water, to a plasma arc torch 402, which can besubstantially the same as the torch of FIGS. 1 and 2. As shown, thesupply system 400 includes a liquid source 404 and a liquid supplyconduit 406. The liquid source 404 can be a container (e.g., a tank) forstoring a supply of shield liquid, such as water. The liquid supplyconduit 406 can be configured to conduct the liquid from the liquidsource 404 to the torch 402. For example, the liquid supply conduit 406can be in fluid communication with the liquid passageway 306 tointroduce the shield liquid to the flow region 302. A set of pump andmotor 418 can be connected between the liquid source 404 and the torch402 along the liquid supply conduit 406 to mechanically pass the shieldliquid through the conduit 406. In some embodiments, a bypass releasevalve 420 is connected between the liquid source 404 and the torch 402and in parallel to the pump and motor set 418 to establish a bypass path422. As an example, for a 130-ampere process, the water pressure can beabout 40 pounds per square inch (PSI) at a flow rate of 14 gallons perhour. As another example, for a 60-ampere process, the water pressurecan be about 40 PSI at a flow rate of 12 gallons/hour. The bypassrelease valve 420 acts as a relief valve by returning, if needed, all orpart of the liquid discharged by the pump and motor set 418 back toeither the liquid source 404 or the inlet of the pump. This is done toprotect the pump and any associated equipment from excessive liquidpressure. The bypass release valve 420 and the bypass path 422 can beinternal (an integral part of the pump and motor set 418) or external(i.e., installed as a separate component in the fluid path).

In addition, one or more components can be coupled to the liquid supplyconduit 406 to regulate properties associated with the supply of theshield liquid from the source 404 to the torch 402. For example, anactivation valve 408 (e.g., a solenoid valve) can be coupled to theliquid supply conduit 406 and disposed between the liquid source 404 andthe torch 402 to enable or disable a flow of the liquid to the torch402. A pressure gauge 416 can be coupled to the liquid supply conduit406 to measure the liquid pressure associated with a flow of the shieldliquid in the liquid supply conduit 406. A pressure regulator 410 can becoupled to the liquid supply conduit 406 to regulate the liquid pressureassociated with a flow of the shield liquid in the liquid supply conduit406, such as by increasing or decreasing the liquid pressure to achievea desired pressure value. A flow meter 414 can be disposed between theliquid source 404 and the torch 402 along the liquid supply conduit 406to measure a flow rate of the flow of the liquid in the liquid supplyconduit 406. A flow valve 412 (e.g., a needle valve) can be coupled tothe liquid supply conduit 406 to regulate a flow rate of the flow of theliquid in the liquid supply conduit 406, such as by increasing ordecreasing the liquid flow rate to achieve a desired flow rate.

Among the components that can be coupled to the liquid supply conduit406 to regulate various liquid supply properties, the supply system 400can include a set comprising the pressure regulator 410, the flow valve412, the activation valve 408 and the flow meter 414 (optional) in oneexemplary configuration. In another exemplary configuration, the supplysystem 400 includes the pressure regulator 410, the activation valve408, and the flow meter 414 (optional). In yet another exemplaryconfiguration, the supply system 400 includes the flow valve 412, theactivation valve 408 and the flow meter 414.

FIG. 4 shows another exemplary fluid supply system of the presenttechnology. The supply system 500 can deliver a shield liquid (e.g.water) or a shield gas (e.g., nitrogen) to a plasma arc torch 502 usingan activation valve 508. The plasma arc torch can be substantially thesame as the torch of FIGS. 1 and 2. As shown, the supply system 500includes a liquid source 504 and a liquid supply conduit 506 that isconfigured to conduct a liquid from the liquid source 504 to theactivation valve 508. The liquid supply conduit 506 and the liquidsource 504 can be substantially the same as the liquid supply conduit406 and the liquid source 404 of FIG. 3, respectively. In addition, thesupply system 500 can include a set of pump and motor 518 connectedbetween the liquid source 504 and the activation valve 508 along theliquid supply conduit 506 and a bypass release valve 520 in parallel tothe pump and motor set 518 to establish a bypass path 522. Thesecomponents can function substantially the same as their counterpartcomponents of FIG. 3. In some embodiments, a shield liquid from atraditional liquid supply source, such as water supplied by publicutilities, can be delivered to a plasma arc torch, instead of using areservoir and a pump.

The supply system 500 also includes a gas supply system 530 (e.g., a gasselection console, a metering console, a gas source, etc.) and a gassupply conduit 532 that is configured to conduct a gas (e.g., N₂ or air)from the gas supply system 530 to the activation valve 508. The supplysystem 500 further includes a shield fluid conduit 534 formed by joiningthe gas supply conduit 532 and the liquid supply conduit 506 downstreamfrom the activation valve 508 (e.g., liquid metering equipment). Upon auser selection from a computerized console (not shown) coupled to thesupply system 500, the activation valve 508 can allow either (i) allowthe shield liquid to flow from the liquid source 504 through the liquidsupply conduit 506 to the torch 502 via the fluid supply conduit 534, ifa shield liquid is selected by the user, or (ii) shut off the liquidflow to allow the shield gas from the gas supply system 530 to flow fromthe gas supply conduit 532 to the torch 502 via the fluid supply conduit534, if a shield gas is selected by the user. Hence, the shield fluidconduit 534 can convey one of the shield gas from the gas supply conduit532 or the shield liquid from the liquid supply conduit 506 to the flowregion 302 of the torch 502 depending on an operator selection.

In addition to the activation valve 508, one or more components can becoupled to the shield liquid conduit 506 to regulate propertiesassociated with the supply of the shield liquid to the torch 502. Forexample, a pressure gauge 516 can be coupled to the liquid supplyconduit 506 to measure the pressure associated with a flow of the shieldliquid in the shield liquid conduit 506. A pressure regulator 510 can becoupled to the shield liquid conduit 506 to regulate the pressureassociated with a flow of the shield liquid in the shield liquid conduit506, such as by increasing or decreasing the pressure to achieve adesired pressure value. A flow meter 514 can be coupled to the shieldliquid conduit 506 to measure a flow rate of the flow of the liquid inthe shield liquid conduit 506. A flow valve 512 (e.g., a needle valve)can be coupled to the shield liquid conduit 506 to regulate a flow rateof the flow of the liquid in the shield liquid conduit 506, such as byincreasing or decreasing the liquid flow rate to achieve a desired flowrate.

Among the components that can be coupled to the shield liquid conduit506 to regulate various liquid supply properties, the supply system 500can include a set comprising the pressure regulator 510, the flow valve512, the activation valve 508 and the flow meter 514 (optional) in oneexemplary configuration. In another exemplary configuration, the supplysystem 500 includes the pressure regulator 510, the activation valve508, and the flow meter 514 (optional). In yet another exemplaryconfiguration, the supply system 500 includes the flow valve 512, theactivation valve 508 and the flow meter 514.

FIG. 5 shows an exemplary method for operating the plasma arc torch ofFIGS. 1 and 2. As shown, the method 600 starts when a plasma gas ispassed to a plasma chamber in the plasma arc torch (step 602). Theplasma gas can be introduced into the torch through the inlet gasopening 235 of the swirl ring 105 into the inner gas chamber 175. Theplasma gas is then directed to the distal outlet gas port 135 thatprovides the gas from the inner gas chamber 175 to the plasma chamber130. In some embodiments, the distal outlet gas port 135 can generate asubstantially swirling plasma gas flow in the plasma chamber 130.

Once the plasma gas reaches the plasma chamber 130, a first portion ofthe plasma gas is ionized to form a plasma arc in the plasma chamber 130(step 604). In some embodiments, another portion of the plasma gas inthe plasma chamber 130 can remain in its unionized form as an unionizedplasma gas. As the plasma arc and/or the unionized plasma gas isexpelled from the plasma chamber 130 via the nozzle exit orifice 195, aportion of the plasma gas can be diverted through the venting channel180 and directed to at least one vent gas passage 125 in the nozzle 100(step 606).

The plasma arc, along with the unionized plasma gas, can be expelledfrom the gas chamber 130 to the flow region 302 via the nozzle exitorifice 195 (step 608), where the flow region 302 is situated betweenthe nozzle 100 and the shield 300. A shield liquid can be supplied tothe flow region 302 via a passageway 306 located between the nozzle 100and shield 300 using, for example, the fluid supply system 400 of FIG. 3or the fluid supply system 500 of FIG. 4 (step 610). The flow region 302can expel the shield liquid, along with the plasma arc and/or theunionized plasma gas, to the outside via the shield exit orifice 304.The shield liquid can form a column about the plasma arc and/or theunionized plasma gas to substantially surround them as they are ejectedvia the shield exit orifice 304 (step 612). In some embodiments,constriction on the plasma arc can be provided by at least one of (i)the swirling motion of the plasma gas in the plasma chamber 130, (ii)the nozzle exit orifice 195 as the plasma arc exits therethrough, (iii)the shield liquid as it surrounds the plasma arc when passing throughthe shield exit orifice 304 and (iv) the venting of the unionized plasmagas provided by the venting channel 180.

FIG. 6 shows cut results on exemplary stainless steel workpieces usingthe systems and methods described above with reference to FIGS. 1-5.Cutting is performed on four 10-gauge stainless steel workpieces using aplasma arc torch operated at a current of 60 ampere and vented throughthe nozzle. The plasma arc torch, similar to the torch of FIGS. 1 and 2,is equipped with a set of consumables including an electrode, a swirlring, a nozzle and a shield. For the first workpiece 702, the cuttingprocess uses only nitrogen (N₂) as the plasma gas and no shield fluid.For the second workpiece 704, the cutting process uses N₂ as both theplasma gas and shield gas. For the third workpiece 706, the cuttingprocess uses a mixture of 95% nitrogen and 5% hydrogen (F5) as theplasma gas and N₂ as the shield gas. For the fourth workpiece 708, thecutting process uses N₂ as the plasma gas and water (H₂O) as the shieldliquid. In addition, the plasma arc torch is equipped with a cap having18×0.0156 diameter holes (i.e., 18 holes of 0.0156 inch diameter) and a0.040 inch counterclockwise offset during the cutting process.

As shown, by using a liquid (i.e., water) as the shield fluid and N₂ asthe plasma gas, the fourth workpiece 708 has better cut appearancecompared to the first workpiece 702 or the second workpiece 704, wherethe edge of the cut is close to the base metal color and dross free. Thefourth workpiece 708 shows similar cut appearance to the third workpiece706. The superior cut achieved by the fourth workpiece 708 is obtainedat a higher cut speed in comparison to the cutting speed of the otherworkpieces. For example, a 50% increase in speed is achieved in thecutting of the fourth workpiece 708 using the N₂/H₂O combination incomparison to the cutting of other workpieces. Specifically, the cuttingspeed is increased from 95 inches per minute (“ipm”) to 135 ipm.

In addition, it is evident from the third workpiece 706 that at leastsome of the hydrogen in the F5 plasma gas interacts with the shield gasN₂ to impart a silver-like color to the cut edge. In the N₂/H₂O processas reflected by the fourth workpiece 708, at least some of the hydrogenfrom water and/or vapor of the shield liquid can interact with the N₂plasma gas to give the cut edge an appearance and color closer to thebase metal. In contrast, for the N₂/N₂ process as reflected by thesecond workpiece 702, the cut edge is much darker, which is indicativeof nitride formation.

FIG. 7 shows cut results on exemplary aluminum workpieces using thesystems and methods described above with reference to FIGS. 1-5. Cuttingis performed on two ¼-in thick aluminum workpieces using a plasma arctorch, equipped with a set of consumables including an electrode, aswirl ring, a nozzle and a shield. For the first workpiece 802, theplasma arc torch is vented, the cutting process applies a cuttingcurrent of 60 ampere, and the cutting process uses N₂ as the plasma gasand water as the shield liquid. In addition, the plasma arc torch isequipped with a cap having 18×0.0156 diameter holes (i.e., 18 holes of0.0156 inch diameter) and a 0.040 inch counterclockwise offset duringthe cutting process. For the second workpiece 804, the plasma arc torchis not vented, the cutting process applies a cutting current of 130ampere, and the cutting process uses a mixture of 35% hydrogen and 65%argon (H35) and N₂ as the plasma gas and N₂ as the shield gas. As shown,using water as shield fluid, combined with vented nozzle, providesbetter cut quality on an aluminum workpiece (e.g., the workpiece 802)than a gas as shield fluid with non-vented nozzle. In addition to asignificant cutting speed increase (i.e., same speed for half theamperage), the appearance of the cut edge for the workpiece 802 is farbetter (i.e., smoother and cleaner) in comparison to the workpiece 804,which is cut by a non-vented, 130 ampere process that uses a combinationof H35 & N2 as plasma gas and N2 as shield gas.

FIG. 8 shows cut results on another set of stainless steel workpiecesusing the systems and methods described above with reference to FIGS.1-5. Cutting is performed on four ½-inch thick stainless steelworkpieces using a plasma arc torch operated at 130 ampere. The plasmaarc torch is equipped with a set of consumables including an electrode,a swirl ring, a nozzle and a shield, similar to the torch of FIGS. 1 and2. To cut the first workpiece 902, the plasma arc torch is not vented.The cutting process uses H35 as the plasma gas and N₂ as the shield gaswith a cutting speed of 30 ipm. To cut the second workpiece 904, theplasma arc torch is not vented. The cutting process uses a combinationof H35 and N₂ as the plasma gas and N₂ as the shield gas with a cuttingspeed of 30 ipm. To cut the third workpiece 906, the plasma arc torch isnot vented. The cutting process uses N₂ as the plasma gas and H₂O as theshield gas with a cutting speed of 45 ipm. To cut the fourth workpiece908, the plasma arc torch is vented. The cutting process uses N₂ as theplasma gas and H₂O as the shield gas with a cutting speed of 60 ipm. Asshown, there is a 50% cutting speed gain between the non-vented processwhere water is used as a shield fluid (e.g., represented by the thirdworkpiece 906) and the non-vented processes where a gas is used as ashield fluid (e.g., represented by the first workpiece 902 and thesecond workpiece 904). Furthermore, there is a 100% cutting speed gainbetween the vented process where water is used as a shield fluid (e.g.,represented by the fourth workpiece 908) and the non-vented processeswhere a gas is used as a shield fluid (e.g., represented by the firstworkpiece 902 and the second workpiece 904). Hence, a vented process, incombination with using water as a shield fluid, provides superiorcutting performance than a non-vented process and/or a process with gasas a shield fluid.

FIGS. 9A and B show various views of cut results on yet another set ofstainless steel workpieces using the systems and methods described abovewith reference to FIGS. 1-5. Cutting is performed on two ½-inch thickstainless steel workpieces using a plasma arc torch operated at 130ampere. The plasma arc torch is equipped with a set of consumablesincluding an electrode, a swirl ring, a nozzle and a shield, similar tothe torch of FIGS. 1 and 2. The plasma torch also uses N₂ as the plasmagas and H₂O as the shield gas to process both workpieces. To cut thefirst workpiece 1002, the torch uses a non-vented nozzle with a cuttingspeed of 55 ipm. To cut the second workpiece 1004, the torch uses avented nozzle with a cutting speed of 65 ipm. As shown, the workpiece1004, which is cut by the vented process, is relatively clean and drossfree in comparison to the workpiece 1002, which is cut by the non-ventedprocess. In addition, the cutting speed for the vented process is fasterin comparison to the cutting speed for the non-vented process due tobetter constriction of the plasma arc provided by the venting.Furthermore, cut performance is enhanced when a vented process iscombined with using water as a shield fluid, the result of which isillustrated by the workpiece 1004. This is because the water/vaporproduced by the shield liquid constitutes a denser medium, which assistsin the effective removal of molten metal during cutting, thus resultingin a faster cut speed and cleaner cut surface.

FIG. 10 shows cut results on yet another set of stainless steelworkpieces using the systems and methods described above with referenceto FIGS. 1-5. Cutting is performed on two ½-inch thick stainless steelworkpieces using a plasma arc torch operated at 130 A. The plasma arctorch is equipped with a set of consumables including an electrode, aswirl ring, a nozzle and a shield, similar to the torch of FIGS. 1 and2. To cut the first workpiece 1102, the cutting process is vented, andthe cutting process uses N₂ as the plasma gas and water as the shieldliquid. To cut the second workpiece 1104, the cutting process is notvented, and the cutting process uses H35 as the plasma gas and N₂ as theshield gas. The first workpiece 1102 shows better cut quality (e.g.,smoother cut edge) than the second workpiece 1104 due to the use ofwater as the shield fluid. In addition, because nitrogen and water arereadily available in the industry and are relatively cheaper to obtainthan other fuel materials (e.g., gases such as H35 or F5), the use of N₂as the plasma gas and water as the shield liquid for cutting the firstworkpiece 1102 is cost effective. Hence, the operating cost associatedwith processing the first workpiece 1102 is significantly lower. Inaddition, the heat-affected zone in the first workpiece 1102 issignificantly smaller in comparison to that of the second workpiece1104, which uses nitrogen as the shield gas, as evident by the darkeningnear the edges of the second workpiece 1104.

In general, the cut results illustrated by FIGS. 6-10 show that thecombination of shield gas venting plus using a liquid (especially water)shield fluid provides better cut performance characteristics incomparison to using venting or a shield liquid alone in a cuttingprocess. For example, FIG. 6 shows that a vented process with water asshield fluid (workpiece 708) offers better cutting speed than a ventedprocess with gas as shield fluid (workpieces 702, 704 and 706) andbetter cut edge appearance (e.g., compared to workpieces 702 and 704).Therefore, a vented process with water as shield fluid providesgenerally good quality cuts at a higher speed when compared to a ventedprocess with gas as shield fluid. In addition, FIG. 8 shows that avented process with water as shield fluid (workpiece 908) offersimproved cutting speed and cut edge appearance than a non-vented processwith water as shield fluid (workpiece 906). FIG. 8 further shows that avented process with water as shield fluid (workpiece 908) performsbetter in terms of speed in comparison to a non-vented process with gasas shield fluid (workpieces 902 or 904) while maintaining similar cutappearances. Thus, unexpected superior cutting results can be achievedby using a combination of venting and a shield liquid in a cuttingprocess.

FIG. 11 shows a percentage-speed improvement comparison chart for threedifferent processes (with various combinations of venting and shieldfluid usage) on aluminum workpieces of about the same quality. Thecomparison is based on the percentage of speed improvement of eachprocess in relation to a base process, which is a non-vented processwith gas as shield fluid. As shown, percentage improvement 1202corresponds to a vented process with gas as shield fluid, percentageimprovement 1204 corresponds to a non-vented process with water asshield fluid, percentage improvement 1206 corresponds to an expectedimprovement for a vented process with water as shield fluid, andpercentage improvement 1208 corresponds to the actual improvement forthe same vented process with water as shield fluid. As illustrated,using a combination of venting and a shield liquid (e.g., water) in acutting process produces the largest speed improvement over the baseprocess, as demonstrated by percentage improvement 1208, which is evenhigher than the expected improvement 1206.

FIG. 12 shows a cutting speed comparison chart for four differentprocesses (with various combinations of venting and shield fluid usage)on stainless steel workpieces of about the same quality. The comparisonis based on 100 times the measured speed of each process normalized bythe operating current of the process. The speed can be in the unit ofinches/minute. As shown, speed 1302 (e.g., a normalized speed)corresponds to a non-vented process with gas as shield fluid, normalizedspeed 1304 corresponds to a vented process with gas as shield fluid,normalized speed 1306 corresponds to a non-vented process with water asshield fluid, and normalized speed 1308 corresponds to a vented processwith water as shield fluid. As illustrated, using a combination ofventing and a shield liquid (e.g., water) in a cutting process producesthe highest normalized cutting speed, as demonstrated by normalizedspeed 1308.

FIG. 13 shows a comparison of workpiece surface roughness and wavinessproduced by four different processes (with various combinations ofventing and shield fluid usage) on aluminum workpieces of about the samequality. As shown, values 1402 a and 1402 b correspond to mean Rz (meanheight of roughness profile) and mean Wz (mean height of wavinessprofile), respectively, for a 60-ampere vented process with F5 as plasmagas and N₂ as shield fluid. Values 1404 a and 1404 b correspond to meanRz and mean Wz, respectively, for a 130-ampere non-vented process withH35 and N₂ as plasma gas and N₂ as shield fluid. Values 1406 a and 1406b correspond to mean Rz and mean Wz, respectively, for a 60-amperevented process with N₂ as plasma gas and H₂O as shield fluid. Values1408 a and 1408 b correspond to mean Rz and mean Wz, respectively, for a130-ampere vented process with air as both plasma gas and shield fluid.As illustrated, using a combination of venting and a shield liquid(e.g., water) in a cutting process produces the lowest surface roughnessand waviness, as demonstrated by values 1406 a and 1406 b.

It should also be understood that various aspects and embodiments of theinvention can be combined in various ways. Based on the teachings ofthis specification, a person of ordinary skill in the art can readilydetermine how to combine these various embodiments. In addition,modifications may occur to those skilled in the art upon reading thespecification. The present application includes such modifications andis limited only by the scope of the claims.

What is claimed is:
 1. A method for operating a plasma arc torch to cuta workpiece, the method comprising: passing a plasma gas to a plasmachamber in the torch defined by an electrode and a nozzle, ionizing afirst portion of the plasma gas to form a plasma arc in the plasmachamber; venting a second portion of the plasma gas via at least onevent passage disposed in the nozzle; passing the plasma arc from theplasma chamber to a flow region via a nozzle exit orifice, the flowregion defined by the nozzle and a shield; supplying a liquid to theflow region via a conduit located between the nozzle and the shield; anddirecting the liquid from the flow region to surround the plasma arc. 2.The method of claim 1, wherein ionizing the first portion of the plasmagas further comprises passing a current between the electrode and thenozzle.
 3. The method of claim 1, further comprising constricting theplasma arc by the venting.
 4. The method of claim 1, further comprisingconstricting the plasma arc by the nozzle exit orifice before it passesto the flow region.
 5. The method of claim 1, further comprisingconstricting the plasma arc by surrounding the plasma arc with theliquid by the shield exit orifice.
 6. The method of claim 1, furthercomprising shearing, by the liquid, in a liquid or vapor state, moltenmaterial away from a workpiece being processed by the plasma arc.
 7. Themethod of claim 1, further comprising reducing, by the liquid, a heataffected zone generated during processing of a workpiece by the plasmaarc.
 8. The method of claim 1, further comprising directing the liquidfrom the flow region to surround the plasma arc such that the liquidsurrounds and constricts the plasma arc.
 9. The method of claim 1,further comprising constricting the plasma arc by both the venting andthe directing of the liquid to surround the plasma arc.
 10. The methodof claim 1, further comprising receiving, by a liquid passageway locatedbetween the nozzle and the shield, the liquid having a liquid swirlstrength from a liquid source.
 11. The method of claim 10, wherein theconduit located between the nozzle and the shield is the liquidpassageway that supplies the liquid to the flow region.
 12. The methodof claim 10, further comprising activating a valve disposed between theliquid source and the torch along a liquid supply conduit to enable aflow of the liquid to the flow region via the liquid passageway.
 13. Themethod of claim 12, further comprising regulating a liquid pressurevalue associate with the flow of the liquid in the liquid supplyconduit.
 14. The method of claim 12, further comprising regulating aflow rate of the flow of the liquid in the liquid supply conduit by aflow valve disposed between the liquid source and the torch along theliquid supply conduit.
 15. The method of claim 12, further comprisingmeasuring a flow rate of the flow of the liquid in the liquid supplyconduit by a flow meter disposed between the liquid source and the torchalong the liquid supply conduit.
 16. The method of claim 12, furthercomprising: supplying a shield gas from a gas source to the flow regionvia a gas supply conduit; and conveying one of the shield gas from thegas supply conduit or the liquid from the liquid supply conduit to theflow region via a shield fluid conduit based on an operator selection,wherein the shield fluid conduit is configured to join the gas supplyconduit and the liquid supply conduit downstream from the activationvalve.
 17. The method of claim 1, wherein the plasma gas is at least oneof nitrogen, F5 or air.
 18. The method of claim 1, wherein the liquid iswater.
 19. The method of claim 1, wherein a combination of the plasmagas and the liquid produces hydrogen.
 20. The method of claim 1, whereinthe liquid introduced to the shield has low or no swirl.